This invention relates to high performance semiconductor device packaging.
Semiconductor devices increasingly require lower cost packaging with higher thermal and electrical performance. A common package used for high performance devices is the Plastic Ball Grid Array (“PBGA”). The PBGA is a surface mount package that can provide higher thermal and electrical performance, and a lower thickness profile and a smaller footprint, as compared to leadframe based surface mount packages such as Plastic Quad Flat Package (“PQFP”) and others. Improvements are sought in the structure and design of the package, to provide increased thermal and electrical performance and to maintain the established footprint and thickness characteristics of standard PBGAs.
In conventional PBGAs a small fraction of the heat generated by the semiconductor device dissipates to the ambient through the molding compound, principally at the upper surface of the package, and, to a much lesser extent, through the sides. Most of the heat that is generated by the semiconductor device in standard PBGAs is conducted through the solder balls to the product board, and the board acts as a heat sink.
Various approaches have been employed or suggested for increasing power dissipation from PBGAs. For example, power dissipation to the ambient can be increased by blowing air over the package; but cost considerations or space limitations may make such air cooling approaches impractical. And, for example, power dissipation can be increased by increasing the number of solder balls between the package and the board, and, particularly, by increasing the number of balls directly beneath the device; and by using a laminate substrate having multiple metal layers. These approaches require increases in package dimensions and changes in the package structure.
In another approach to increasing power dissipation from PBGAs, often referred to as “Thermally Enhanced PBGA” or TEPBGA, a partially embedded metal heat spreader is employed. The partially embedded metal heat spreader includes an upper generally planar portion having a top surface free of the molding compound and exposed to ambient; and embedded portions, which may be referred to as supporting arms, extending from the upper portion downward to the substrate and attached at the lower ends to the upper or die support surface of the substrate.
Conventionally, TEPBGAs having partially embedded heat spreaders are formed generally as follows. A completed ball grid array is provided, with the die attached on the die support surface of the substrate and connected to the substrate, e.g. by wire bonds. A heat spreader is placed on the support surface of the substrate over the die, with the heat spreader supporting arms rigidly affixed onto the supporting surface using, for example, a cement or adhesive, such as an epoxy cement or adhesive or glue. Then this assembly is placed over a mold cavity in an injection mold, so that the upper surface of the upper portion of the heat sink is at the bottom of the mold cavity and the substrate surface contacts the edges of the upper opening of the mold cavity. Then the molding compound is injected into the cavity, where it encloses the die and the wire bonds and the supporting arms of the heat spreader and fills the space between the upper surface of the die and the upper portion of the heat spreader. The molding material hardens to form the mold cap, and the completed assembly is released from the mold.